/Engine/Plugins/Online/OnlineFramework/Source/Party/Public/SocialToolkit.h
Finds a SocialUser given a unique net ID from any OSS
[USocialUser](API\Plugins\Party\User\USocialUser) * FindUser ( const [FUniqueNetIdRepl](API\Runtime\Engine\GameFramework\FUniqueNetIdRepl) & UserId ) const